Actually, I've just recalculated it and it is almost break even with the diesel being £200 cheaper over 4 years / 100,000 miles! It just depends if you want higher finance payments I guess. With the diesel you are paying for the fuel up front - with the petrol you keep more cash in your bank account.
Here is how I [roughly] work it:
1.2 Reference Sport = £8595 OTR
1.4 Reference Sport Tdi = £10,395 OTR
Petrol : 100,000 (160,934km) x 0.955 litre (@ 5.9 litres per 100km) = £9067
Diesel: 100,000 (160,934km) x 0.975 litre (@ 4.6 litres per 100km) = £7217
* Petrol prices are todays average price on
www.petrolprices.com
I used parkers to get the p/x price of the car 4 years old - same model - but could only get the value with 30,000 miles on the clock as you have to pay extra to adjust the mileage.
It isn't exactly scientific but is the best I can do!
Petrol
====
£8595 cost of car
£1177 interest on HP
£9067 fuel cost
=====
18839
-3355 p/x car at end
-100 interest you got on your money in bank
====
15384
Diesel
====
£10395 cost of car (1.4 Reference Sport TDi)
£1424 interest on HP
£7217 fuel cost
=====
19036
-3895 p/x car at end
=====
15141